Structure and method for manufacturing compact optical power monitors of highly reliable performance

0001This Formal Application claims a Priority Date of Mar. 15, 2002 benefited from a Provisional Application 60/364,983 filed by the same Applicant of this Application on Mar. 15, 2002.

FIELD OF THE INVENTION

0002This invention relates generally to a device configuration and method for making optical power monitors. More particularly, this invention relates to a simplified device configuration and method for manufacturing optical monitor to provide reliable performance.

BACKGROUND OF THE INVENTION

0003A technical challenge is faced by those of ordinary skill in the art of designing and manufacturing optical devices to provide compact and reliable optical sensing and monitoring devices including power monitors with application versatility that can be conveniently implemented in different optical systems to carry out the self monitoring and diagnostic functions. Specifically, as the optical network communication systems are more broadly employed to perform signal transmissions with higher bandwidths while various optical systems are becoming more complicate, the maintenance and trouble shooting of the optical systems become more difficult. For the purpose of reducing communication downtime and the costs required for system maintenance, diagnoses and repairs, there are ever increasing demands of “smart” systems provided with the self-monitoring, diagnostic and even self-correcting functions. A first step moving toward such systems is to introduce more sensing and monitoring devices in different optical system to carry out continuous sensing and detections of system and operation conditions. The sensor and monitors are implemented not only in the new systems but often are also required in the existing systems as well. Installation of sensors and monitors into existing systems often requires the use of smaller size sensors and monitors with broader range of operation versatility to fit into the existing configurations and operation conditions. Conventional techniques of optical sensing and monitoring devices are not able to provide the sensors and monitors with sufficient compactness, versatility and reliability, including the optical power monitors, suitable for such applications.

0004For these reasons, there is still a need in the art of design and manufacture of optical power monitors with smaller size, more operational versatilities and higher reliability to overcome the difficulties discussed above. Specifically, an improved and simplified configuration and method for making smaller and reliable optical power monitors with reduced production cost are required.

SUMMARY OF THE PRESENT INVENTION

0005It is therefore an object of the present invention to provide a new and improved simplified and reliable configuration and manufacturing method to provide compact and reliable power monitor device such that the above-mentioned difficulties and limitation can be resolved. This invention discloses a method to simplify the manufacture processes by forming the tapping layer as optical splitting/tapping layer directly on the GRIN lens without alignment and assembling processes. Furthermore, the new and improved configuration and manufacture method take advantage of the optical path deviations between incident/reflection beams through a GRIN lens when there is a small linear shift between the optical axes of the fiber pigtail and GRIN lens. More reliable power monitor device with reduced insertion loss can be achieved with new and improved alignment method implemented with a set of holding tubes to achieve minimum insertion loss between the incident and reflective beams.

0006Specifically, it is an object of the present invention to provide a simple and reliable device to sample and monitor signals in an optical system. The power monitor is implemented with a filter-centered packaging design to achieve high environmental stability. Integration of the tapping and detection elements is implemented as part of the design to achieve a compact device configuration and to simplify the processes of device manufacture. The new and improved configuration also utilizes concurrent light collecting and focusing functions to improve the signal collection efficiency. The concurrent light collecting and focusing unit is packaged as part of a hermetically sealed sensor housing to provide flexibility of selecting sensors with various degrees of sensitivities and response time. The power-sensing device disclosed in this invention is therefore useful not only for signal intensity detection but also for other broader ranges of applications such as data quality analyses. The new and improved device as disclosed in this invention thus provide several key advantages including but not limited to ultra compactness, broad versatility, long term device dependability and reliability, and design flexibility to fit into wide varieties of existing optical systems. The simplified configuration of the device as disclosed in this invention further streamline the manufacturing processes and reduce the production cost of the power sensing devices.

0007Briefly, in a preferred embodiment, the present invention discloses a new optical power monitor. The power monitor includes a collimator for collimating an incident light into a collimated beam. The power monitor further includes a beam splitter/tapping layer for transmitting a tapped portion of the collimated beam through the splitter/tapping layer for detecting an optical intensity. The coated splitter/tapping layer on the collimator further reflects a remaining portion of the collimated beam back to another optical transmitting media for continuous optical transmission.

0008This invention further discloses in a preferred embodiment, a method for monitoring an optical power. The method includes the steps of A) Employing a collimating means for collimating an incident light into a collimated beam. And, step B) of coating a splitter/tapping layer onto the collimating means for transmitting a tapped portion of the collimated beam therethrough for measuring and monitoring an optical power. In a preferred embodiment, the method further includes a step of receiving the incident optical beam through an input optical port of a dual fiber ferrule for projecting to the collimating means and receiving an output optical beam reflected from the splitter/tapping layer through an output optical port of the dual fiber ferrule. In another preferred embodiment, the method further includes a step of receiving the tapped portion of the collimated beam from the beam splitting/tapping layer into an optical signal detecting means for detecting an optical intensity.

0009These and other objects and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment, which is illustrated in the various drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

0010<figref idref="DRAWINGS">FIG. 1</figref> is a cross sectional view of a schematic diagram showing the structure of a power monitor of this invention;

0011<figref idref="DRAWINGS">FIG. 2</figref> is a schematic diagram for showing vertical shift between two holding tubes for adjusting the relative position of the dual fiber ferrule and the GRIN lens to adjust the input and output beam projections; and

0012<figref idref="DRAWINGS">FIG. 3</figref> is cross sectional view of two alternate shapes of holding tubes for housing and holding different sizes of focusing and sensing units.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

0013Referring to <figref idref="DRAWINGS">FIG. 1</figref> for a preferred embodiment of an optical power monitor <b>100</b> of this invention. The improved power monitor <b>100</b> includes a dual fiber ferrule <b>110</b> to receive an input beam from an input optical fiber <b>106</b> and projecting an output beam from an output optical fiber <b>107</b>. The input beam received from the input optical fiber <b>106</b> is projected into a beam collimator <b>120</b>, e.g., a GRIN lens <b>120</b> coated with a filter coating <b>125</b>. The filter coating <b>125</b> functions as a beam splitting-taping filter to transmit a tapped portion of the beam through a focus lens <b>130</b> onto a photo-detector, e.g., a photodiode <b>140</b> for measuring the intensity of the beam received form the input optical fiber <b>106</b>. The splitting-tapping filter <b>125</b> further reflect a major portion of the beam back through the GRIN lens <b>120</b> onto the output optical fiber <b>107</b> as an output optical beam. The splitting-tapping filter <b>125</b> is formed as a multiple-layered coating deposited onto the focusing surface of the GRIN lens <b>120</b> to maximize the thermal stability and to reduce the optical energy loss thus increasing the optical damage threshold. By coating the splitting-tapping filter <b>125</b> directly onto the GRIN lens <b>125</b> further simplifies the device structure and strengthens the mechanical integrity of the device and eliminates an alignment requirement between the GRIN lens <b>120</b> and a separate optical filter in the case a separate reflecting-tapping device is employed instead of the multi-layered coating filter. The ratio of the light splitting can be adjusted to accommodate different levels of photoelectric signal intensity and total optical signal intensity loss. Typically, the multi-layered filter coating is formed to generate a tapped signal in the range of 1% to 10% of the initial beam intensity.

0014The face-to-face end surfaces <b>101</b> and <b>111</b> of the dual fiber ferrule <b>110</b> and the GRIN lens <b>120</b> respectively are arranged as parallel surfaces with an incline angle θ where θ is eight degrees, i.e., 8°, to increase the return losses. Both of these end surfaces <b>101</b> and <b>111</b> are coated with anti-reflection multi-layered coating to reduce the optical losses in the transmission of the optical signal through these inclined surfaces. In order to adjust for minimizing the signal loss, the dual optical fiber ferrule <b>110</b> and the GRIN lens <b>120</b> are held in two holding tubes <b>105</b> and <b>124</b> respectively. These two holding tubes <b>105</b> and <b>124</b> have parallel interface to assure that there are only lateral linear position adjustments are made between the GRIN lens <b>120</b> and the dual fiber ferrule <b>110</b>. There is an air gap <b>121</b> between the dual fiber ferrule <b>105</b> and the GRIN lens <b>120</b> for focusing optimization. A very small gap <b>123</b> between these two holding tubes allows freedom of lateral movements between two holding tubes <b>105</b> and <b>124</b>. Held by these two holding tubes <b>105</b> and <b>124</b>, the relative position between the GRIN lens <b>120</b> and the dual fiber ferrule <b>110</b> is adjusted along two linear directions without relative angular adjustments thus significantly simplify the alignment processes. These two linear directions are along the optical axis, i.e., the X-axis and the Y-axis perpendicular to the optical axis, i.e., the Z-axis, to minimize the optical loss between the input port <b>106</b> and the output port <b>107</b>.

0015<figref idref="DRAWINGS">FIG. 2</figref> showed the alignment schematic. The relative movement between dual fiber ferrule <b>105</b> and GRIN lens <b>120</b> along the principle axis Z contributes to the focusing condition adjustments. Meanwhile, the relative lateral movements in the plane that contains X-axis and Y-axis change the angle between collimated incident beam and principle axis Z. Therefore, the relative position of incident beam and output beam can be adjusted by 3-dimention alignment. In a preferred embodiment, the separation between the input and output optical fiber <b>106</b> and <b>107</b> is about 125 μm. The angle between the direction of the light beam emitted from the splitting-tapping filter coating <b>125</b> and the principle axis of the device along the Z-axis α is about 1.8°.

0016Referring to <figref idref="DRAWINGS">FIG. 1</figref> again, for the purpose of increasing the structure integrity, a third holding tube <b>150</b> is holding the GRIN lens and the focus lens <b>140</b>. The holding tube contained also a photodiode <b>140</b> that has a hermetic sealing metal housing <b>160</b> to seal the holding tube and the photodiode <b>140</b> from the rear end of the holding tube <b>150</b>. The physical size of active area of the sensor determines the dark current and the capacitance and these functional parameters also respectively affect the signal to noise ratio (S/N) and the analog response bandwidth. In order to achieve higher S/N ratio and fast response, it is desirable to lower the capacitance and the dark current and in turn, that can be achieved by reducing the active area of the photodiode <b>140</b>. However, larger active area of the photodiode <b>140</b> can increase the overall response of the detector since more area will be illuminated. A balanced approach is to achieve adequate S/N ratio and response speed up to 2 GHz by adjusting the active area in the range from 50 μm to 100 μm in diameter. For a specific embodiment, the beam size of the light emitted from the beam splitting-tapping filter <b>125</b> is around 300 to 500 μm in diameter. In order to produce a compact power-monitoring device, it is necessary to apply a focus lens <b>130</b> with a short focus length to reduce the size of the detector <b>140</b> and the optical path from the splitting-tapping filter <b>125</b> to the detector <b>140</b>. One specific configuration as shown in <figref idref="DRAWINGS">FIG. 1</figref> is to use a short focus lens <b>130</b> that is part of the hermetically sealed house <b>160</b>. A silica ball lens is implemented in a preferred embodiment to obtain low cost and good performance. To further reduce the space requirement for an even more compact power monitor, a specially designed aspherical lens may also be employed.

0017By using the holding tube <b>150</b> and the seal housing <b>160</b>, fixing the focus lens <b>130</b> and the photodiode <b>140</b> at fixed locations within the seal housing <b>160</b>, a self-aligned configuration is provided that greatly simplify the manufacture processes. The time and cost of manufacture is reduced and better structural integrity and product reliability is also achieved. As the tapped beam is focused onto the photodiode <b>140</b>, the photo energy is converted into electric energy by generating corresponding amount of photoelectric current that can be converted directly as light intensity measurement through two electrodes <b>145</b>. The photo-detector <b>140</b> can be further integrated by providing preamplifier onto the photo sensor chips to allow for even more flexibilities to process the tapped optical signal.

0018According to <figref idref="DRAWINGS">FIGS. 1</figref> to <b>3</b> and above descriptions, this invention discloses an optical power monitor. The power monitor includes a collimating means <b>120</b> for collimating an incident light into a collimated beam. The power monitor further includes a beam splitter/tapping means for transmitting a tapped portion of the collimated beam therethrough for measuring and monitoring an optical power wherein the beam splitter/tapping means comprising a splitter/tapping layer <b>125</b> coated onto the collimating means. In a preferred embodiment, the power monitor further includes a dual fiber ferrule <b>110</b> having an input optical port <b>106</b> for receiving an incident optical beam to project to the collimating means <b>120</b>, the dual fiber ferrule further having an output optical port <b>107</b> for receiving an output optical beam reflected from the splitter/tapping means. In another preferred embodiment, the power monitor further includes an optical signal detecting means <b>140</b> for receiving the tapped portion of the collimated beam from the beam splitting/tapping layer for detecting an optical intensity. In another preferred embodiment, the optical signal detecting means further includes a focal lens <b>130</b> for focusing the tapped portion of the collimated beam onto a photodiode <b>140</b> for detecting an optical intensity. In another preferred embodiment, the power monitor further includes a first holding tube <b>105</b> for holding the dual fiber ferrule <b>110</b> and a second holding tube <b>124</b> for holding the collimating means <b>120</b> wherein the first holding tube and second holding tubes having a lateral position adjustment gap for minimizing an optical loss of the output optical beam reflected from the splitter/tapping means. In another preferred embodiment, the power monitor further includes a third holding tube <b>150</b> for holing the collimating means and the optical signal detecting means <b>140</b> for securely fixing a relative position therein. In another preferred embodiment, the power monitor further includes a seal housing <b>160</b> for sealing a rear opening of the third holding tube opposite the collimating means wherein the seal housing holds the focal lens <b>130</b> and the photodiode <b>140</b> at fixed positions for plugging and sealing the rear opening and placing the focal lens substantially at an optimal position relative to the splitting/tapping layer. In another preferred embodiment, the focal lens is a silica ball lens. In another preferred embodiment, the focal lens is an aspherical lens. In a preferred embodiment, the collimating means is a GRIN lens having an inclined lens surface relative to a main optical axis of the GRIN lens and the inclined lens surface facing a parallel ferrule surface of the dual fiber ferrule wherein the lens surface is disposed at a gap-distance from the parallel ferrule surface for achieving a focus optimization.

0019This invention further discloses a method for monitoring an optical power. The method includes the steps of A) Employing a collimating means for collimating an incident light into a collimated beam. And, step B) of coating a splitter/tapping layer onto the collimating means for transmitting a tapped portion of the collimated beam therethrough for measuring and monitoring an optical power. In a preferred embodiment, the method further includes a step of receiving the incident optical beam through an input optical port of a dual fiber ferrule for projecting to the collimating means and receiving an output optical beam reflected from the splitter/tapping layer through an output optical port of the dual fiber ferrule. In another preferred embodiment, the method further includes a step of receiving the tapped portion of the collimated beam from the beam splitting/tapping layer into an optical signal detecting means for detecting an optical intensity.

0020In a preferred embodiment, this invention further discloses a method of monitoring an optical power. The method includes the steps of A) employing a collimating and tapping means for tapping a tapped portion of an optical signal to a focusing and detecting means for detecting the tapped portion of the optical signal. B) Employing a holding tube for securely holding and fixing the collimating and taping means at a fixed relative position from the focusing and detecting means. And, step C) employing a seal housing for sealing a rear opening of the holding tube opposite the collimating and tapping means and holding the focusing and detecting means in the seal housing for plugging and sealing the rear opening and placing at an optimal position relative to the collimating and tapping means.

0021This invention further discloses a seal housing <b>160</b> for searing a rear tube opening of a holding tube <b>150</b>. The seal housing <b>160</b> includes at least two optical components held by the seal housing at fixed positions for plugging and sealing the rear tube opening provided to proper function with a third optical component inserting from a front tube opening opposite the rear tube opening. In a preferred embodiment, the seal housing holding a focus lens <b>130</b> and a photo-sensor <b>140</b> at fixed positions. In another preferred embodiment, the holding tube <b>150</b> is provided for holding a GRIN lens <b>120</b> placed therein from a front opening of the holding tube <b>150</b>.

0022The holding tubes <b>105</b>, <b>124</b> and <b>150</b> are securely attached to the dual fiber ferrule <b>110</b>, the GRIN lens <b>120</b> and the GRIN lens and the seal housing <b>160</b> respectively by applying thermally cured epoxy for long term reliable structure integrity and operation stability. The end surfaces between the holding tubes <b>105</b> and <b>124</b> are also securely attached together with properly applied adhesive material such as epoxy for fixing the relative position for minimizing the optical losses. The thermal stability and long term performance reliability of the power monitor <b>100</b> is dependent on several structural and functional parameters. Specifically, these parameters are 1) the degree of fitness between the holding tubes and the dual fiber ferrule and the GRIN lens, 2) the length of the holding tubes <b>105</b> and <b>124</b>, 3) the quality of the end surfaces and the strength of mutual attachment of the holding tubes, 4) the uniformity of the interface between the holding tubes <b>105</b> and <b>124</b>, 5) the material of the holding tubes <b>105</b>, <b>124</b> and <b>150</b>, 6) the types and the amount of the adhesive applied; 7) the pre-treatment of the end-surfaces to function as bonding surfaces; and 8) the settlement and curing processes of the adhesives for bonding the holding tubes thus bonding the device together. These interfaces and quality of attachment are greatly improved according to the configuration disclosed in this invention because the simple and linear interface configuration without curved or irregular shaped interface surfaces with proper freedom of movement for flexible position adjustment and conveniently application of adhesive materials on these interfaces.

0023Although the present invention has been described in terms of the presently preferred embodiment, it is to be understood that such disclosure is not to be interpreted as limiting. Various alternations and modifications will no doubt become apparent to those skilled in the art after reading the above disclosure. Accordingly, it is intended that the appended claims be interpreted as covering all alternations and modifications as fall within the true spirit and scope of the invention.